Pyrolytic cracking and thermo-catalytic cracking have been used to convert waste plastics, petroleum sludge, slope oil, and vegetable oil into lower hydrocarbons. However, many of the processes and devices used to achieve this conversion have failed to produce useful end products efficiently and economically to be commercially viable.
Pyrolytic cracking typically refers to a process in which higher hydrocarbons are heated to elevated temperatures of up to about 800° C. at which chemical bonds break to form lower hydrocarbons. To achieve these elevated temperatures, a large amount of energy is involved. Typically, the cost of the energy involved outweighs the value of end products produced. Certain existing implementations for pyrolytic cracking use molten metal baths as a heating medium for achieving elevated temperatures. However, achieving these elevated temperatures using molten metal baths tends to be inefficient in terms of cost and maintenance. Moreover, the use of molten metal baths poses occupational health hazards, given the tendency of metals to oxidize over time. Other existing implementations carry out a pyrolysis stage, which is then followed by a catalytic conversion stage to convert higher hydrocarbons into lower hydrocarbons. However, such implementations continue to suffer from the use of elevated temperatures and large amounts of energy during the initial pyrolysis stage.
Thermo-catalytic cracking typically refers to a process of converting higher hydrocarbons into lower hydrocarbons in the presence of a set of catalysts, such that the process can be carried out at lower temperatures than those typically involved in pyrolytic cracking. There have been a few unsuccessful attempts to incorporate thermo-catalytic cracking in a commercially viable plant that can convert higher hydrocarbons into lower hydrocarbons. There are a number of unresolved technical challenges faced by existing implementations, including handling more than one type of feedstock, rendering the process substantially continuous, determining a composition of a set of catalysts for optimal yield at lower cracking temperatures, delivery of feedstock into a cracking device, removal of residue from the cracking device, and tuning the quality and quantity of resulting end products. In addition, thermo-catalytic cracking poses a number of process design challenges, such as designing a cracking device to achieve optimal heat transfer area, selection of a heating medium, avoiding or reducing under-utilization of heat transfer area typically encountered in a batch processing mode due to depleting level of feedstock, effective removal of residue in the cracking device that can lead to poor heat transfer, and mitigating coke formation on a heat transfer surface of the cracking device. These challenges hinder the ability to scale up equipment size for commercially viable plants.
It is against this background that a need arose to develop the process for thermo-catalytic cracking and related devices and systems described herein.